Differential Diagnosis of Mr. B

Question 1:

1) Left-sided headaches

2) Right-sided weakness (4/5 strength)

3) Bruises on right arm and leg

4) Lethargic

5) Decreased fluency of spontaneous speech

6) Unsteady/stumbling

7) Increased reflexes in right arm and leg

8) Right Babinski’s sign

9) Falls (for past month)

10) Alcohol abuse

Question 2: (main source used: BASIC MOTOR PATHWAY)

Mr B’s condition appears to involve the corticospinal tract, as it is in control of motor function in the body and plays a role within the somatosensory pathway. ‘Corticospinal tract’ is the name of the primary motor pathway, which starts in the precentral gyrus in the cortex and ends in the spine. The precentral gyrus represents most of the tract but other cortical areas contribute as well.

The corticospinal tract starts from the axons of pyramidal neurons in layer V of the primary motor cortex. Once these axons leave the pyramidal cells, they enter the white matter just below layer VI of the primary motor cortex. The ‘corona radiata’ can be found deeper in the brain, and is what the white matter merges into to form one large body of axons. The ‘corona radiata’ delves into the deep nuclei of the brain, splitting the caudate and the putamen – at this point the axons become the ‘internal capsule’. This ‘internal capsule’ is particularly vulnerable to strokes.

Sensory information travels through the internal capsule coming up from the thalamus to the cortex, while motor information travels through it on its way down to the spine. It has an anterior and posterior limb – the sensory and motor information travels through the posterior limb. The internal capsule can be found in the midbrain, where the axons are called ‘cerebral peduncles’ or ‘stalks of the cerebrum’ - which contain all descending axons going to the brainstem or spine. Unlike the internal capsule, they are mostly one-way and almost all of them are heading south. The ascending axons take other routes to get to the thalamus.

Once the midbrain gives way the pons, one of two things may happen to the peduncle: many of the axons from the cortex that were headed to the pons synapse will get off and synapse or the remaining corticospinal axons fragment within the pons - they are no longer visible as a tight bundle, though they can be seen as several smaller bundles.

In the medulla, the fibers come together again as the ‘pyramids’. The pyramids run the entire length of the medulla – large, uninterrupted axon tracts on the ventral surface. The fibers of the pyramid cross at the start of the cervical spine, known as the ‘Decussation’ of the pyramids.